Tribological properties and scratch healing of a typical automotive nano clearcoat modified by a polyhedral oligomeric silsesquioxane compound

• A hydroxyl-functional POSS was employed as reinforcing agent.
• POSS was added to the acrylic/melamine clearcoat formulations to replace OH functional groups of acrylic in the formulations.
• Scratch resistance of the resultant clearcoats improved due to increase in hardness and XLD.
• Scratches on the nanocomposites were healed thank to the POSS capability to physically interact with the surrounding matrix.
• The clarity of the clearcoat remained intact in presence of POSS.

The present work has studied the influence of an OH-functionalized polyhedral oligomeric silsesquioxane(POSS) nano-structure on the scratch resistance of a typical acrylic melamine clearcoat. Scratch resistance and the healing ability of clearcoats were investigated by micro-scratch studies and confocal profilometry techniques. In addition, hardness and thermo-mechanical characteristics of clearcoats were investigated by micro-indentation and dynamic mechanical thermal analysis (DMTA) respectively, to correlate the scratch behavior to the mechanical and structural properties of the clearcoats. The results revealed that incorporation of POSS cages into clearcoats could effectively enhance the scratch resistance. This was attributed to the higher hardness and cross-linking density of the resulting nanocomposite coatings. The healing results also demonstrated that nanocomposites had a higher healing ability compared to the neat clearcoat. The higher healing of nanocomposites was explained by the physical H-bonding interactions formed in vicinity of POSS cages. The transparency measurements proved that these improvements were fulfilled without any negative effect on the optical quality of clearcoats.

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